The synthesis and photophysical studies of cyclometalated Pt(II) complexes with C,N,N-ligands containing imidazolyl donors

Two new C,N,N-type ligands (HL2 and HL3), containing a C-phenyl, a N-pyridyl, and a N-imidazolyl donor, and their cycloplatinated complexes, [Pt(L-2)Cl] (1), [Pt(L-3)Cl] (2), [Pt(L-2)(PPh3)](+) (3) and [Pt(L-3)(PPh3)](+) (4), have been successfully synthesized and characterized. Spectroscopic and 3MLCT luminescent properties of these Pt(II) cyclometalated complexes were found to be pH dependent. This was attributed to the protonation/deprotonation of the acidic 1-imidazolyl-NH moieties on the ligands. All the cycloplatinated complexes (both protonated and deprotonated forms) possessed two-photon excitability with two-photon absorption cross-sections ranging from 6.0 to 30.0 GM(protonated forms) and from 16.2 to 24.9 GM (deprotonated forms).